This invention relates to ratchet switches and, more particularly, to switches which will alternately make and break a circuit upon actuation of a pawl. Switches of this type are widely used as foot switches on commercial and domestic vacuum cleaners. One such widely used ratchet switch includes a pawldriven ratchet wheel and a switch wheel driven by the ratchet wheel. The switch wheel is provided with a plurality of electrically connected contact plates spaced about the periphery of the wheel and separated circumferentially by an insulating material. Contact arms are biased against the periphery of the switch wheel to alternately make and break a circuit as the switch wheel is driven by the ratchet wheel. The ends of the contact arms contact the plates and the arm has a preshaped or unstressed curvature which concavely faces the contact plate. Each time the blade wipes across a plate, some metal is lost from its tip, due to frictional wear and due to arcing between the plate and the arm. The tip, therefore, is worn away in a direction of increasing clearance between the arm and the plate, resulting in an increasing loss of arm deflection. As arm deflection is lost, contact pressure decreases with a resulting increase in arm and contact plate operating temperatures as the switch is cycled. Underwriters' Laboratories requires that a switch maintain a temperature less than 30.degree. C. over ambient temperature. It has been determined, however, that the previously described prior art switch will rise above the 30.degree. C. limitation in less than 15,000 cycles.
As the prior art arms shorten, they reach a length in which there is substantially no contact pressure between the arm and its plate, so that as the arm snaps toward the plate, it will momentarily touch the contact and then release. This causes the vacuum cleaner or other associated appliance to be momentarily pulsed, with attendant degradation of the motor and substantial arcing.
Furthermore, since the arms act as an escapement mechanism on the ratchet wheel, tending to bias the wheel in a proper position against the pawl, a substantially even wear on both arms will result in the switch wheel's changing its predetermined rotative position with respect to the arms. As the contact pressure is decreased moreover, the pawl and ratchet mechanism becomes less and less positive.